The present invention relates to cleaners or filters in general, particularly to liquid filters. Still more particularly, the invention relates to improvements in liquid filters of the type wherein a metal housing or case for filter elements is sealingly connected with a chamber or cup which consists of nonmetallic material. Such filters or cleaners (also known as filterboxes) are often used for removing impurities from liquid fuels.
It is already known to connect a plastic cup with a metallic housing or case for filter elements by means of threads. Such types of connections between a metallic case and a nonmetallic cup are leakproof and exhibit a satisfactory resistance to pressures in spite of the fact that the thermal expansion coefficient of the metallic part is different from that of the nonmetallic part. However, a satisfactory sealing action can be achieved only if the threads on the metallic and nonmetallic parts are machined with a relatively high degree of precision which contributes significantly to initial cost of the filter. Moreover, the seal between the case and the cup is likely to deteriorate in response to repeated separation of the case which contains interchangeable filtering elements.
It was further proposed to utilize expendable cases for filtering material. Such cases can be connected with a glass cup by means of an elastic washer and an O-ring. The rather expensive glass cup can be reused, i.e., a case containing clogged filtering elements can be detached and replaced with a case containing fresh filtering elements. A drawback of the just described filter is that its cost is relatively high. Thus, it is normally necessary to use a fresh O-ring and a fresh washer whenever a case containing clogged filtering elements is to be replaced with a fresh case. Moreover, the replacement of a spent case with a new one takes up a relatively long interval of time and the person wishing to replace a spent case is likely to forget to keep a supply of spare washers and O-rings. Still further, an unskilled person is likely to connect a fresh case in such a way that the connection between the case and the glass cup allows leakage of liquid which can present a serious danger if the leaking liquid is a fuel.